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Diazene, a Potential New Hydrogen Bond Donor and Acceptor with Blue-Shifted N-H Stretching Modes: A Theoretical Study

Karpfen A., Liedl E., Wolschann P.

Polish Journal of Chemistry

2009

Vol. 83, nr 5

933-942

The structure and vibrational spectra of hydrogen-bonded complexes formed between trans-HNNH (diazene or diimide) and the fluoromethanes CH3F, CH2F2, and CHF3 are stud ied at the MP2/6-311++G(2d,2p) level. For each fluoromethane, complex structures were detected in which diazene plays either the role of a hydrogen bond do nor or a hydrogen bond acceptor. In addition to the well-known blue shifts of the fluoromethane C–H stretch ing frequencies, blue-shifted N–H stretching frequencies are predicted for the diazene molecule, irrespective of whether HNNH acts as do nor or acceptor. It is shown that this finding can be interpreted as a consequence of the negative intramolecular coupling (NIC) between N–N and N–H stretching degrees of free domin the isolated HNNH molecule which, upon complex formation, leads to a negative intramolecular response (NIR)

FT-IR Studies of CH...B Interactions in Fluoroform Containing Cryosolutions

Melikova S., Rutkowski K. S., Rodziewicz P., Koll A.

Polish Journal of Chemistry

2002

Vol. 76 / nr 9

1271-1285

A transition from a blue shifted frequency of the _(CH) vibrations of CF3H to a conventional red frequency shift, accompanied by unusually varying integrated intensity of the corresponding _1 band, have been studied in CF3H/B systems, where B = Ar, N2, CO, CO2, O(CD3)2, NH3, and N(CD3)3. DFT/B3LYP and ab initio MP2 calculations, utilizing the 6-311++G(3df,3pd) basis set, predict a weakly H-bond-like linear F3CH…B complex formation in the series studied and reproduce experimentally observed variations of spectroscopic parameters. The results obtained are treated in the framework of induced dipole moment, taking into account opposite directions of the CH bond dipole moment and the dipole moment of the whole molecule. In the range of overtone and combination bands of fluoroform, new weak bands have been detected. They were attributed to simultaneous excitations of vibrations of interacting CF3HandB(=CO,CO2) molecular pairs.